In fuel injectors the valving mechanism typically comprises a reciprocal valve element that seats on and unseats from a valve seat. Sealing of the valve element to the valve seat, when the fuel injector is closed, is important in avoiding fuel leakage, or drip. Since the sealing is attained by only metal-to-metal contact, the shapes of the valve element and the seat are especially important. A valve element which has a spherical contoured surface for seating on a frusto-conical valve seat has been found to provide effective sealing. Various designs have been proposed for embodying a spherically contoured surface in a fuel injector valve element.
In one known design, the distal end of a cylindrical needle is shaped to have essentially a semi-spherical surface. In another known design, a truncated sphere (slightly larger than a semi-sphere for example) is the valve element. In still another known design, an entire sphere is joined to one end of a tube. The use of any of these designs affects the fuel injector cost because they require joining and/or metalworking operations in order to make the valve element.
The use of a simple sphere is advantageous because such spheres can be economically fabricated with precision in large volumes. Because of the cost disadvantages which are inherent in the known designs just described, it would be beneficial if a fuel injector could incorporate a sphere without the injector fabrication process requiring joining and/or metalworking of the sphere. In other words, it would be advantageous if the sphere is nothing more than a part which is merely assembled into a fuel injector during the assembly process.
Another factor that contributes to the cost of known fuel injector designs, such as those in which the spherical contoured surface is at one end of an elongated member, is the necessity of securing precise alignment of the valve member to the seat. Precision metalworking operations must be conducted on several individual parts, and assembly of the parts must be carefully performed. Even with the use of sophisticated manufacturing techniques, today's mass-production of fuel injectors still results in a significant percentage which are unable to meet engineering performance specifications when tested after assembly. These injectors must be then re-worked, resulting in added cost.
A still further consideration in fuel injector design is the desire to miniaturize fuel injectors for certain uses. Fuel injectors which are presently in commercial production are not large parts, but the market is seeking injectors which are even smaller. Such miniaturized fuel injectors will require smaller individual parts, and because such parts are more difficult to process, manufacturing complexity is likely to be amplified. This is a further reason why the use of a simple sphere as the valve element would be desirable.
The present invention relates to a new and improved electrically-operated fuel injector which utilizes a simple sphere as the valve element. The process for fabricating the fuel injector does not require the use of joining or metalworking operations on the sphere: the sphere is simply one of the individual parts of the fuel injector. The organization and arrangement of the fuel injector provides for the inherent self-alignment of the sphere to the valve seat while avoiding the precision finishing operations required to secure the accurate alignment of the valve element with the valve seat in known fabrication procedures. The organization and arrangement is also adapted to render the fuel injector well-suited for miniaturization.
As a consequence, the invention provides a fuel injector which is electrically operated, and which can be miniaturized, but without incurring prohibitively expensive manufacturing costs. Further features, advantages, and benefits of the invention will be seen in the ensuing description and claims which are accompanied by drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.